In the days after 17 people died in a mass shooting at a Florida high school, the teenage survivors announced their intent to converge on Washington, D.C., for a March for Our Lives. The idea for an anti-gun-violence statement spread, and March 24 events were quickly planned in cities across the country.

Except in San Francisco. When Shoshana Ungerleider went online a couple days after the Feb. 14 shootings at Marjory Stoneman Douglas High School in Parkland, Fla., to see what was planned for the famously activist city, she was amazed to find ... nothing.

So Ungerleider, a hospital-based physician, and her husband posted a message on social media inviting friends to join them at San Francisco City Hall this Saturday to support the youth movement.

“We were just so taken with what we saw on the news, seeing these students come out in a very forceful way saying, ‘Enough is enough,’” Ungerleider said.

She has coordinated professional conferences before, but she’s never organized a mass demonstration. This first one is going to be tough to top.

The couple’s friends forwarded the social media invitation to their friends. Within three days, 25,000 people said they were coming. Now, city officials have told her that as many as 100,000 people could attend the rally at Civic Center Plaza and march to the Embarcadero.

The main march in Washington has generated big-name support, including large donations from Salesforce chief executive Marc Benioff; actor George Clooney and his wife, Amal; actress Kate Capshaw and her husband, producer and director Steven Spielberg; and Oprah Winfrey.

The national fundraising effort for the D.C. rally has collected nearly $3.4 million in just over a month. The idea has spread overseas, with gatherings planned in Vietnam, Israel, Lithuania, Australia and the Indian Ocean island nation of Mauritius. A handful of counterprotests have also been announced, including pro-gun-rights rallies in Utah, Montana and Indiana.

An anti-gun-violence protester in Olympia, Wash., on March 6, holds signs promoting the March 24 rallies around the nation and the world.

Photo: Ted S. Warren, Associated Press

Hollywood stars aren’t behind the San Francisco effort — it’s strictly a regular-person proposition. Ungerleider, 37, has scrambled to get permits, portable toilets, water trucks and whatever else is needed to accommodate a mass gathering. She put her hospital work on hold for a month to gather adult and teenage volunteers and plan the event.

“We have to capitalize on this momentum,” she said, and so, “I’ve learned how to order Porta-Pottis.” Eighty of them.

She and her volunteer organizer colleagues have raised nearly $33,000 of their $45,000 goal online to help cover costs. She hopes to break even, and if there’s any money left over, it will go to the gun-reform organization Moms Demand Action.

Come Saturday, the event itself will keep young people “front and center,” Ungerleider said. Although adults are helping to organize the event, the grown-ups will be limited to supporting roles, she added.

“Every adult onstage is there to introduce a student,” Ungerleider said.

The ninth-grader at Crystal Springs Uplands School, a private school in Hillsborough, said she is growing up in a world where mass shootings happen far too often. She hopes the March for Our Lives will “make change in the future.”

Like the students in Parkland, she believes young people need to lead that effort.

“This is definitely a student event,” she said. “It’s important it’s a student event.”

In Oakland, young people will also be at the center of a morning rally at Frank Ogawa Plaza, with a couple of politicians, although “not too many,” said organizer Sevan Apollo. He leads youth workshops promoting empathy and compassion.

“We want them to use their voices,” Apollo said. “If they’re old enough to get shot by bullets, they’re old enough to have opinions.”

Among the scheduled speakers are students from Young, Gifted and Black, a poetry-focused youth performing arts group, along with members of the Oakland Youth Advisory Commission and Stoneman Douglas High alumni who live in the Bay Area, Apollo said.

Organizers expect a few thousand people to attend the 10 a.m. rally, with participants then heading to San Francisco for the 1 p.m. rally and march.

“We don’t even know how many people are coming,” Ungerleider said. “My hope for this is it will be a very inspiring day.”

Jill Tucker has covered education in California for 18 years, writing stories that range from issues facing Bay Area schools districts to broader national policy debates. Her work has generated changes to state law and spurred political and community action to address local needs.

She is a frequent guest on KQED’s “Newroom" television show and "Forum" radio show. A Bay Area native, Jill earned a master’s degree in journalism at the University of Colorado, Boulder and a bachelor’s degree from the UC Santa Barbara. In between, she spent two years as a Peace Corps volunteer teaching English in Cape Verde, West Africa.